It has been common knowledge for centuries that air columns of differing length produce musical notes of differing pitch. An example of an instrument based upon this principle is a pipe organ. Such organs have a multiplicity of pipes of varying lengths (as well as diameters) but the length of a particular pipe (and the air column therein) does not change.
Other examples include cornets and trumpets which use linearly-actuated valves and French horns which use rotary valves, all to change the note(s) produced by the instrument. In these latter examples, such note changes are by valving tubing of various lengths into or out of the air column "circuit," thus changing the length of the air column as measured from the instrumentalist's lips to the bell from which sound is emitted.
Trombones and tubas are yet other examples of instruments producing different notes by changing the air column length. A trombone uses a telescoping handslide to change the length of the air column. And many trombones (often referred to as slide trombones) use only a handslide for that purpose.
(By way of parenthetical background, it should be appreciated that the lower the note being played with, for example, a trombone, the longer is the air column and the more difficult it is for the musician to achieve "volume" in the note being played. This is so because the longer air column creates increased resistance to air passage.)
A feature of a slide trombone is that the handslide must often be manipulated very rapidly between notes. And, sometimes, it must be manipulated quickly over a relatively great distance as, for example, when playing a higher note (at which time the handslide is close to the musician's face and fully telescoped or nearly so) followed immediately by a low note requiring the handslide to be extended well away from the musician.
To help reduce the time required to play certain sequential notes, rotary valves have been developed to switch one or more lengths of tubing into and out of the instrument air column. This quickly effects a change in air column length (and, therefore, a note change) by valve manipulation rather than by handslide manipulation.
It is believed that the first rotary valve was invented in about 1832 by one Mr. Joseph Riedl of Vienna, Austria and in any event, disc-shaped rotary valves have been in wide use since at least as early as the late 1930's. Such valves are mounted on the instrument so that a flat, circular surface is toward the musician's cheek and does not interfere with or touch the musician's cheek.
Although rotary valves solved one problem, they were attended by new problems. For example, common disc-shaped rotary valves have pieces of tubing (those switched into and out of the circuit by the valve) fastened to the valve casing generally radially and using rather sharp bends. And the internal valve passages themselves involved some rather sharp bends. These "convolutions" in the air flow path add yet additional resistance to the musician's "blowing power." Thus, they not only further limit the maximum volume that a musician can obtain, they also have some undesirable effect on tonal quality.
Yet another difficulty with known rotary valves is that even though the stationary tubing attached to the valve casing is circular in cross-section, the passages in the rotating valve piston are often ellipsoid (or, perhaps of some other shape) but not circular. As a result, there is an abrupt flow discontinuity where the non-circular passage and the circular tube intersect. The tonal quality of the instrument is thereby adversely affected. Such a valve is said to lack "flow tangency."
The currently-available Model YSL-682B trombone, made by Yamaha Corporation, includes an example of a rotary valve which (in addition to being ill-suited for two-valve instruments) lacks flow tangency. The stationary tubing attached to the valve is circular in cross-section but the passage through the valve piston is distinctly D-shaped.
And the tubing attached to the valve casing not only includes at least one rather sharp bend adjacent to the casing, such tubing "wraps" over an arc of about 270.degree. and introduces added resistance to air flow. A bend in such tubing protrudes from the bottom of the instrument and uncomfortably into the shoulder of the musician.
Further, the Yamaha valve introduces two bends in each of two air flow passages when the valve is in the switched position for playing lower notes. Since the switched position provides a longer air column, these bends introduce flow resistance at that time when the musician is least able to tolerate them and overcome their resistive effect. Like the Thayer valve discussed below, the Yamaha valve is a relatively new design introduced in an effort to resolve some of the shortcomings of earlier valves.
A few years ago, a rotary valve known as the Thayer valve was introduced, apparently to help overcome the problem of lack of flow tangency. The Thayer valve uses a cone-shaped rotating piston with an air entry passage at the apex end. The air exit passage terminates at the cone base (as does another passage in this two-passage valve) and such terminations are spaced radially outward from the cone center axis through the apex end and perpendicular to the base.
A difficulty with the Thayer valve is that at that portion of the valve adjacent to the base of the piston, the valve is quite thick and usually (and annoyingly) contacts the musician's cheek. In fact, it is not an exaggeration to say that the valve sometimes uncomfortably "digs into" the musician's cheek.
Still another difficulty with the Thayer valve involves the matter of valve lubrication. In professional use, trombone valves are usually lubricated daily. To lubricate the Thayer valve, one must substantially disassemble the instrument and this is annoying and time-consuming.
Still another difficulty with conventional rotary valves involves the matter of weight. The starting material for the rotating pistons of known disc-shaped rotary valves is a solid bar or rod of brass. Passages are milled or otherwise formed in the rod.
A new rotary valve for brass instruments (and method for making such a valve) which offers straight-through flow passages, which does not interfere with the musician's person, which uses only gradual bends and which is light in weight would be an important advance in the art.